So the question is, what current cards, that don't see much play, do you expect to see in tournaments/gauntlet? Here are mine:

B/W: Oberon's Eulogy--could see a Shin'hare deck that finally has the tools for this.D/W: Iljun's Parade (+ Major Diamond Gem of gain life = defense)--perfect in the Forever's Child 'go wide' deck.R/B: Claw of the Mountain God--hard to call this one since the archetype has been spoiled the least. I'd like to hear from some of the people who played the set at the invitational to get a better idea of exactly what R/B is trying to do. If it's 'damage matters', then Claw of the Mountain God is in a great place as an under-costed 3 drop which provides reliable self damage and survives Electrofry. S/R: Yesterday--Actions matters decks are going to need to play this as a 'get out of jail free' card to give them time for their engines to come online. Zygmunt's Game's presence in the same decks will discourage opponents from following up with their best, most expensive troop.S/D: Phoenix Guard Messenger--If buffing Flight troops is going to be a thing in constructed, then this is a body in the air that the opponent won't want to remove. Shardless: Forgotten Monarch--likely to be a free play on turn 4, this will be a nice toolbox for these decks.

...And just for fun:

Chants/Constants: It depends heavily upon what the rest of the chants are; currently, I'd have to say that Circle of Preservation is great since it's a replayable constant in Diamond, which has access to Solitary Exile and Soul Marble. However, if the Sapphire Chant is, as you would expect, a low-cost constant that reads, "When a constant enters play under your control, draw a card." And the Ruby chant deals damage when a constant enters, then I'd have to give it to Incantation of Ascendance. Ruby and Sapphire would then have a nice suite of constants that work together in the two chants, Mindpyre, Cerebral Fulmination, and Incantation of Ascendance, along with the removal/disruption to give them time to work.

Chants/Constants: It depends heavily upon what the rest of the chants are; currently, I'd have to say that Circle of Preservation is great since it's a replayable constant in Diamond, which has access to Solitary Exile and Soul Marble. However, if the Sapphire Chant is, as you would expect, a low-cost constant that reads, "When a constant enters play under your control, draw a card." And the Ruby chant deals damage when a constant enters, then I'd have to give it to Incantation of Ascendance. Ruby and Sapphire would then have a nice suite of constants that work together in the two chants, Mindpyre, Cerebral Fulmination, and Incantation of Ascendance, along with the removal/disruption to give them time to work.

Kismet's Reverie definitely seems to be an interesting choice for a Chant deck. Even more so for a PvE one seeing how it doubles the effect when equipped.

many of those cards all fall in the same category, they are good, but too slow.
Just like cerberus, high tomb lord, gront the infinite, army of the arcande cinder and what not. If you play them on turn 5, then get the first bonus on turn 6...it is simply too slow.
Especially in PvE where some games already end after only 3 turns.

many of those cards all fall in the same category, they are good, but too slow.
Just like cerberus, high tomb lord, gront the infinite, army of the arcande cinder and what not. If you play them on turn 5, then get the first bonus on turn 6...it is simply too slow.
Especially in PvE where some games already end after only 3 turns.

we have to hope that later PVE content will have more encounters like the goliath, where you have a huge incentive to build up a amazing board or build up for a OTK.

Those are the limited archetypes though...and while it might help create a top tier deck in the Standard format, usually it isn't enough to break through other more broad archetypes that will now have 4 sets of cards to fuel them. For example thus far we've only really seen the Set 1 R/S Robots/Dwarves deck and the Set 3 R/W 5 cost+ ramp deck that really was a limited archetype that became a good base for a top tier deck in constructed.

So I think it would also be interesting opening up this discussion to what Set 3 cards in limited will be much better now that these will be the limited archetypes people are looking to build.

B/W: Sudden Awakening -- Works extremely well with cards like Trufflehead. D/W: Invigorating Breeze -- Was an ok trick you picked up on the tail end of a pack but now it will have a second very relevant use. Honorable mention to Mesa Lookout that went from a good card to a REALLY good card.R/B: Bombwright -- A bit slow but just like Invigorating Breeze, he becomes twice as good as before in certain decks.S/R: Arcane Focus -- Goes from something you pick up on the wheel to something you actively seek.S/D: Windspeaker -- Not really related to the Flight theme but an absolute gem in the archetype.
Shardless: Sepulchra Bonewalker -- Probably no comment necessary for this one.

Those are the limited archetypes though...and while it might help create a top tier deck in the Standard format, usually it isn't enough to break through other more broad archetypes that will now have 4 sets of cards to fuel them. For example thus far we've only really seen the Set 1 R/S Robots/Dwarves deck and the Set 3 R/W 5 cost+ ramp deck that really was a limited archetype that became a good base for a top tier deck in constructed.

Discussion of limited or constructed is fine. I'm in a constructed mindset right now, so I find it more intriguing to look at some of the cards that feel powerful but unsupported. I'm curious to see what cards people have always wanted to use.